Lubricant



'Patentcd .Aug. 14, 1945 LUBRICANT Frederick B. Downing, Penns Grove, N. J., and Howard M. Fitch, Wilmington, Del., assignors to E. I. du Pont de Nemours 8; Company, Wilmington, Del., a corporation of Delaware No Drawing. Application June 5, 1943,

Serial No. 489,808

8 Claims.

This invention relates to lubricants and particularly to lubricating oils suitable for heavy duty service'in internal combustion engines.

The successful lubrication of internal combustion engines is complicated by the deterioration of the lubricating oil during use. This deterioration, which appears to result primarily from oxidation of the oil, causes the formation of undesirable products not initially present in the oil,

One effect of such deterioration is the formation of the oil, which also interferes with its free circulation. Another effect is the formation of lacquer-like deposits on moving parts, which deposits interfere with free motion and often cause seizure of the parts during operation or when starting. A further effect of such deterioration is the formation of by-products-principally acidic in nature-that corrode sensitive bearing metals such as bearings composed of alloys or mixtures of copper and lead, cadmium and nickel, cadmium and silver or cadmium and tin.

I operation of the engine, is the necessity for frequent and expensive oil changes and reconditioning of the engine, including replacement of sensitive hearings, to prevent mechanical failure of the engine. These effects are particularly noticeable in so-called heavy duty service, that is, in the operation of trucks, buses and other mobile or stationary power plants where a heavy load is applied to the engine and deterioration of the oil is accelerated.

Many materials have been proposed for addition to lubricating oils to prevent oxidation and the formation of sludge therein during storage. Such materials are frequently called antioxidants or oxidation inhibitors. They are frequently quite effective under storage'conditions, but are very much less effective under the conditions of service in an internal. combustion engine. In general, they do not materially inhibit corrosion of sensitive bearing metals by the oils. Other compounds, called corrosion inhibitors, have been proposed for inhibiting-the corrosion of sensitive bearings by the. oils. These corrosion inhibitors generally are not very effective for inhibiting the formation of sludge or preventing the deposition of materials on the parts of the engine.

tergent properties,- for the purpose of removing deposited sludge and lacquers from the engines and to maintain any sludge, formed in the oil, in a fine dispersion therein. Generally, such detergents have little or no antioxidant or corrosion inhibiting properties. It is, therefore, generally necessary to add three or-more different materials to an oil to obtain the desired results.

It is an object of the present invention to provide improved lubricating oils which have been stabilized against the detrimental effects of deterioration due to oxidation. Another object is to provide lubricating compositions for internal combustion engines whereby the formation of sludge and lacquers on the engine parts will be largely eliminated. A further object is to provide lubricating oils for internal combustion engines which contain materials effective for inhibiting the corrosion of sensitive bearing metals in the engine. A still further object is to provide a method for improving the operation of lubricating oils in internal combustion engines, particularly under heavy duty service. Other objects are to provide new compositions'of matter and to advance theart. Still other objects will appear hereinafter.

The'above and other objects may be accomplished in accordance with our invention which comprises incorporating, into a hydrocarbon lubricating oil, from 100 to about 1000 parts of 3 iron for each million parts of oil, hereinafter It has also been proposed to incorporate soaplike materials and other materials, having dedesignated as P. P. M. of iron, in the form of oil-soluble ferric dithiocarbamates derived from secondary aliphatic amines consisting of the elements carbon, hydrogen and nitrogen. We have found that such oil-soluble ferric dithiocarbamates are excellent stabilizers for lubricating oils employed in internal combustion engines, particularly under heavy duty service. They prevent the formation of objectionable deterioration products that would normally form in the oil when employed in the engine and maintain The ferric dithiocarbamates of our invention may be represented by the formula wherein R1 and R: represent alkyl, aralkyl or cycloalkyl groups which are similar or dissimilar or R1 and B: may represent a single alkyl group with the terminal carbon atoms joined to the nitrogen to form a heterocyclic ring. The dithiocarbalmic acids are derived from secondary aliphatic amines by reacting the amine with carbon disulfide, preferably in the presence of caustic alkali. Where R1 and R2 represent separate alkyl groups, it will generally be necessary for them to contain a total of at least 6 carbon atoms in order to provide compounds which will be soluble in the lubricating oil to the extent of at least 100 P. P. M. of iron. By an oil-soluble ferric dithiocarbamate, we mean the one which-is soluble in the oil to the extent that it will provide at least 100 P. P. M. of iron in the oil.

The methods, for making metal dithiocarbamates, are well known. They are usually prepared by reacting an amine with carbon dlsulfide and sodium or potassium hydroxide to form the sodium or potassium salt of the dithiocarbamic acid which is then reacted with a salt of the desired metal. For example, ferric dibutyl dithiocarbamate may be prepared by reacting one mole of dibutylamine with one mole of carbon disulfide and one mole of aqueous sodium hydroxide to form sodium dibutyl dithiocarbamate. Three moles of the sodium dibutyl dithiocarbamate are then reacted with one mole of ferric chloride to form ferric dibutyl dithiocarbamate. Other ferric dithiocarbamates, within our invention, may be prepared in a similar manner, using any other secondary aliphatic amine instead of the dibutylamine. The higher melting ferric dialkyl dithiocarbamates may be purified, if desired, by crystallization from a suitable solvent such as benzene,

toluene, acetone, or alcohol. The lower melting ferric dialkyl dithiocarbamates, that are liquid or oily at ordinary temperatures, may be freed of water and inorganic salts conveniently by extraction with a water-immiscible solvent such as benzene or toluene and then isolated by removal of the solvent by distillation. In some cases, it is convenient to extract the ferric dialkyl dithiocarbamat'e from the aqueous reaction mixture directly into a lubricating oil.

For stabilizing lubricating oils, we prefer to employ from 100 to 1000 and, more preferably, from 200 to 500 P. P. M. of iron in the form of a ferric dialkyl dithiocarbamate. Concentrations of iron less than 100 P. P. M. are substantially ineffective. Concentrations of iron greater than 1000 P. P. M. are no more effective than concentrations of 1000 P. P. M. and hence are uneconomical.

- Concentrated solutions of the more soluble ferric dithiocarbamates may be prepared in lubricating oils and subsequently diluted to the concentration desired for use. The less soluble ferric dithiocarbamates may be dissolved in the lubricating oil directly at the concentration desired for use. In either case, solution in the lubricating oil is facilitated by warming and stirring the lubricating oil while the dithiocarbamate is dissolving;

Compounds, such as ferric dipropyl dithiocarbamate, ferric dibutyl dithiocarbamate and ferric methyl amyl dithiocarbamate, in which Ri+R2, in the formula hereinbefore given, contain 8 or less carbon atoms, have relatively low solubilities in the oils and would not ordinarily be employed as concentrates. Ferric dibutyl dithlocarbamate contains 8.36% of iron. Accordingly, 0.1196% of this compound would be required in the oil to give P. P. M. of iron and 1.196% would be required to give 1000 P. P. M. of iron. However, this compound has been found to be soluble in the oils tested in the extent of only about 0.3%, corresponding to about 250 P. P. M. of iron, although it might be more soluble in some other oils. Therefore, it will generally be desirable to employ a substantially saturated solution of this compound in the oil. Compounds, such as ferric diamyl dithiocarbamate, ferric di-isoamyi dithiocarbamate, ferric dioctyl dithiocarbamate and the like, wherein R1+Rz, in the formula hereinbefore given, contain a total of 10 or more carbon atoms, are relatively more soluble and may be employed to Produce concentrated solutions in the oils which may be diluted to produce the desired concentration. Also, ferric dialkvl dithiocarbamates, in which the alkyl chains are branched as in ferric di-isoamyl dithiocarbamate, are generally much more soluble than the corresponding straight chain compounds. The ferric diamyl dithiocarbamate, employed in the following tests, was prepared from a mixture of straight chain and branched chain diamyl amines.

The most satisfactory method of determining the stability of lubricants in internal combustion engines is by actual operation of the engine. We employ the following engine test, which correlates well with results obtained in the field. Six-cylinder 1940 and 1941 model Chevrolet engines, fitted with one copper-lead bearing, are operated on a block mounting at a speed of 3150 R. P. M. (equivalent to a road speed of 60 miles per hour) against a load of 35 brake horsepower (equivalent to that obtained in road operation) applied by means of a dynamometer. The oil in the sump is maintained at 280 F. and the cooling jacket liquid at 200 F. The test is run for 66% hours (corresponding to road operation for 4000 miles) except in cases where the oil deterio raltion is so extensive that such. lengthy operation is impractical. The degree of deterioration of the oil in this test corresponds directly to that obtained in equal periods of heavy duty service and is indicative of that observed in longer periods of less severe service.

The following ratings are employed to determine the stability of the oil and its effect on the engine. Samples of the oil used are removed from the crankcase at intervals and analyzed for total sludge (naphtha insolubles) and asphaltenes (chloroform solubles) by the method described in J. Ind. Eng. Chem., Anal. Ed. 6, 419 (1934) and for viscosity rise and neutralization number by the well-known ASTM methods. On the basis of these analyses, the condition of the oil is rated as excellent, good, fair, poor or bad. At the end of the run, the engine is disassembled, inspected and rated as to cleanliness. In the system of cleanliness rating employed, a clean engine would score 100 points. Points are deducted from this score, based on the quantity and quality of sludge and other deposits in various parts of the engine. An engine with a score of about 50 points by this system would be so badly fouled as to be in imminent danger of mechanical failure due to impaired lubricant circulation caused by the presence of large amounts of sludge or other deposits or due to seizure of valve mechanisms or other moving parts. The copper-lead bearing is weighed before and after includes a small loss due to wear.

the test to determine the loss in weight. This copper-lead weight loss (expressed in grams per bearing) is a measure of the corrosive action of the oil on-sensitive bearing metals and also 'The following oils, each obtained from a differentrefiner and selected as being typical of the types employed in ignition-engine lubrication, were used in the tests.

' SAE Visooslt Type grade index A.- Solvent extracted Mid-Continent base m 92 B Solvent extracted Pennsylvania base 107 The marked improvement in oil condition and engine cleanliness and decrease in bearing corrosion, obtained by the use of ferric dithiocarbamates in the lubricant, may be seen from the results of tests made as described above and listed in the following table.

TABLE fications can be made in the compounds, proportions and conditions employed, and in other components of the lubricating on without departing from the spirit or scope of our invention and we intend to claim our invention broadly as in the appended claims.

While the stabilizing action of the ferric dithiocarbamates of our invention is most striking in lubricants, employed for so-called heavy duty service, a similar effect is also obtained in less severe service. Internal combustion engines, in.

' finic base oils as well as in naphthenic and asphaltic base oils. The ferric dialkyl dithiocarbamates may also be employed in conjuction with Efiect'of iron dialkyl dithiocarbamates on oil condition, engine cleanliness and bearing c0r-' rosion P. r. Oilcon- 'Engme Cu-Pbon Additive ironin fif dition gg oil rating mung sion 1. None (avgArun) 0 06% Bad.. 55.0 1.05 A Ferric dibutyldithiocarbamate 200 68% Good.-. 91.0 0.57 A Ferric diamyl dithiocarbamate 500 66% -.do.. 93.0 0.10 A Cobalt dibutyl dith1ocarbainate... 200 66% P0012-.. 96.5 2.73 A Nickel dibutyl dithioearbamate... 200 66% ..do 72.6 1.16 B None. 0 nd.- 63.0 1.20 B Ferric diamyldithiocarbamate 500 6% ExceL- 91.0 0.10 B Cobalt dibutylditbiocarbamate 200 66% P0012. 73.0 1.44

The cobalt and nickel dithiocarbamates are added for comparison. It will be noted that both the cobalt and nickel dithiocarbamates were less effective than iron in improving the oil condition of oil A. In all tests, the cobalt and nickeldithiocarbamates increase corrosion of the bearing metal, whereas, 'the ferric dithiocarbam'ate was very effective to decrease the corrosion of the bearing metals. While the cobalt dithiocarbamate appears to give a better engine score in oil A than did the iron dithiocarbamate, this good engine score coupled with poor oil condition indicates that the cobalt dithiocarbamate functions primarily as a dispersant or detergent rather than as an'oil stabilizer.

The following compounds are illustrative of the ferric dithiocarbamates that may be employed as stabilizers for lubricating oils in accordance with our invention.

Ferric dipropyl dithiocarbamate Ferric dibutyl dithiocarbamate Ferric diamyl dithiocarbamate Ferric dioctyl dithiocarbamate Ferric methyl amyl dithiocarbamate Ferric propyl butyl dithiocarbamate Ferric dicyclohexyl dithiocarbamate Ferric benzyl amyl dithiocarbamate Ferric dibenzyl dithiocarbamate Ferric piperidine dithiocarbamate other additives such as pour. point depressants,

viscosity index improvers. thickeners, detergents I and the like.

We do not know the exact mechanism by which the ferric dithiocarbamates of our invention stabilize lubricating oils. They appear to functionprimarily, if not entirely, through protection of the oil from the deleterious effects of oxidation dining use in the engine. The concentrations of the ferric dithiocarbamates employed are insufilcient to produce any worthwhile detergency or lubricity in the oil, and they appear to function as antioxidants'rather than as detergents or film strength improvers. Furthermore, the lubricating oil compositions disclosed are free-flowing liquid lubricants suitable for crankcase use and are not greases.

The stabilizing action, of the ferric dithiocarbamates of our invention, is very surprising in view of the fact that iron soaps, such as ferric naphthenate, are actually detrimental and accelerate rather than retard deterioration of the oil. The stabilizing action is also not common to the metal dialkyl dithiocarbamates as a class. For example, the diakyl dithiocarbamates of mercury and cobalt function to improve engine cleanliness and oil condition but increase the corrosiveness of the oil to such an extent that their use is not practical. The dialkyl/dithiocarbamates of tin, nickel and zinc, on the other hand, do not appreciably increase the corrosiveengine cleanliness and oil condition but also etrectively inhibit corrosion by the oil.

We claim:

1. A lubricating composition comprising a hydrocarbon lubricating oil having incorppratedi in the form of an oil-soluble ferric dithiocarbamate derived from a secondary aliphatic amine consisting of the elements carbon. hy- I drogen and nitrogen.

therein from 100 to about 1000 P. P. M. iron 2. A lubricating composition comprising a hycarbamate containing a total of at least 8 car- 20 bon atoms in the alkyl groups.

4. A lubricating composition comprising hydrocarbon lubricating oil having incorporated therein from about 200 to about 500 P. P. M. of

iron in the form of an oil-soluble ferric dithio- 25 carbamate derived from a secondary aliphatic amine consisting of the elements carbon, hy-

drogen and nitrogen.

5. A lubricating composition comprising a hydrocarbon lubricating oil having incorporated 9 therein from about 200 to about 500 P. P. M. of

iron in the form of an oil-soluble ferric dialkyl dithiocarbamate containing a total of at least 8 carbon atoms'in the alkyl groups.

7. A lubricating composition comprising a hydrocarbon lubricating oil having incorporated therein from about 200 to about 250 P. P. M. of iron in the form of ferric dibutyl dithiocarbamate.

8. A lubricating composition comprising a hydrocarbon lubricating oil having incorporated therein from about 200 to about 500 P. P. M. of iron in the form of ferric diamyl dithiocarbamate.

FREDERICK B. DOWNING. HOWARD M. FITCH. 

